Clean box

ABSTRACT

A cleanbox that can prevent contamination from not only external sources but also from within the cleanbox from such sources as substrates and internal components of the cleanbox, includes a casing container ( 18 ) formed by a container main body ( 12 ) and a lid member ( 14 ) for hermetically sealing a top opening section of the container main body; a dividing wall ( 20 ) for forming circulation paths having an upstreaming path and a downstreaming paths within the casing container; a substrate holding section ( 24 ) disposed in the upstreaming path for holding broad surfaces of substrates (W) approximately parallel to the upstreaming path; an air filter ( 26 ) and a gas removal filter ( 28 ) disposed upstream in relation to the substrate holding section in the upstreaming path; and a motor-driven fan ( 30 ) housed in the casing container for producing air streams circulating in the circulating paths.

TECHNICAL FIELD

This invention relates to a cleanbox suitable for use in storing ortransporting objects to be processed such as semiconductor wafers,photomasks and hard discs in an ultra-clean environment.

BACKGROUND ART

When transporting/storing substrates to be processed such assemiconductor wafers and photomasks used in production plants forsemiconductor devices, minute amount of dust particles adhering to theobjects such as semiconductor wafers and gaseous impurities existing inthe atmosphere surrounding the objects lead to lower product yield. Suchcontamination problems become more critical as the density of circuitintegration increases. For magnetic discs also, the advent of magneticreluctance head has resulted in significantly accelerating high densityrecording so that product cleanliness is being demanded in terms of notonly dust particles but gaseous impurities. From the viewpoint ofreducing reaction of substrates, convenient means for maintaining lowhumidity are also important during storage of substrates.

The demand for such a clean environment in which to transport/storesubstrates has led to the development of cleanboxes equipped withhigh-efficiency particle air (HEPA) filter and ultra-low penetration air(ULPA) filter working in conjunction with a circulation fan. Also, othertypes of storage devices include replacing the air surrounding thewafers in the cleanbox with high purity nitrogen so as to maintainnon-reacting environment and prevent the growth of native oxide film onthe wafer surface.

However, although those cleanboxes based on HEPA and ULPA filters areable to remove particulate contaminants, they are not capable ofremoving minute amount of organic or inorganic gases. Furthermore, theefficiency of sweeping the environment is reduced and the effects ofclean air in preventing contamination cannot be expect, when thecirculation system allows a large volume of circulated air to flow intothose regions that do not contribute to cleanliness of the environment,or if stagnation occurs within the cleanbox. As for the cleanboxes usinga nitrogen-based atmosphere, such boxes are not able to removeimpurities emanating from the wafers having some type of coating such asphotoresist film, for example, and it also raises a concern related tothe safety of nitrogen atmosphere to workers.

DISCLOSURE OF INVENTION

In view of the problems existing in the current technologies, the objectof this invention is to provide a cleanbox to prevent not onlycontamination that can be introduced from external environment but alsocontamination that can be produced internally from the objects stored inthe cleanbox and component parts of the cleanbox.

The invention relates to a cleanbox comprising: a casing containercomprised of a container main body and a lid member for hermeticallysealing a top opening section of the container main body; a dividingwall for forming circulation paths having an upstreaming path and adownstreaming paths within the casing container; a substrate holdingsection disposed in the upstreaming path for holding broad surfaces ofsubstrates approximately parallel to the upstreaming path; an air filterand a gas removal filter disposed upstream in relation to the substrateholding section in the upstreaming path; and a motor-driven fan housedin the casing container for producing air streams circulating in thecirculating paths.

Accordingly, circulation paths are created within the container, and theflowing streams are purified first by using air filter and a gas removalfilter to remove contaminants physically and chemically and then the airstreams are directed to the substrate holding section, so that, even ifthere are particulate and gaseous sources of contaminants adhering tothe inner walls of the container or to the wafers themselves,contamination of the wafers stored in the substrate holding section canbe prevented. Because the air filter and the gas removal filter in theupstreaming path are placed upstream in relation to the substrateholding section, objects to be cleaned can be readily loaded or unloadedfrom the top section of the container without the fear of causingcontamination to the objects. Also, because the container is quitesusceptible to contamination when the lid is opened or closed, thecontainer lid is placed downstream in relation to the substrate holdingsection, so that any contaminants that may have been brought into thecontainer can be removed long before they can reach the objects.

The filtering membrane of the gas removal filter may be comprised singlyof ion exchange fibers or activated charcoal fibers, or by combiningthese fibers or by activated charcoal particulate embedded in a urethanefoam carrier, or by using integrated filtering unit made by weavingthese fibers together. The filtering system efficiently removes andadsorbs ions such as ammonia present in the air and ionic substancescontained in a mist such as hydrofluoric acid and hydrochloric acid byusing ion exchange fibers and activated charcoal fibers produced byactivation reaction of carbons produced from cellulose, acrylic andlignin group fibers. Ion exchange fibers may be produced byradiation-induced graft polymerization.

According to another feature of the invention, the upstreaming path isformed approximately centrally in the casing container, and merges withthe downstreaming paths formed between the dividing walls and thecontainer main body, by being redirected at a top section and/or abottom section having an arc surface or a spherical surface. By shapingthe top section and/or bottom section into a dome shape having an arcradius or spherical radius, the overall flow is made smooth with nostagnating points, and therefore, the energy required to formcirculating paths is reduced so that one battery is sufficient tooperate the cleanbox for a prolonged period of time. It is preferablethat the radius of curvature be not less than 1.2R when the object waferradius is R.

According to yet another feature, the lid section at the inner surfaceand the container main body at the bottom surface are provided withguiding protrusions for separating the streaming path. Normally, theprofile of such a protrusion is triangular.

According to yet another feature, the circulation paths are providedwith a reverse flow preventing filter in a downstream location to thesubstrate holding section so as to prevent back streaming ofcontaminants from the motor-driven fan. Accordingly, even if the fan isstopped, there is no danger of contaminating the wafers due tocontaminants in the fan unit.

It is preferable that the motor for the motor-driven fan is a dcbrushless motor, because there are no moving parts to generatecontaminants. Furthermore, the motor may be canned in a stainless steelcasing of 0.2 mm thickness, so that the motor is dustless and gas tight,thereby preventing contamination by gaseous substances emitted from thecoils and other parts of the fan.

According to yet another feature, the substrate holding section is acarrier receiving section for freely detachably seating a carrier havingopenings at the top and the bottom sections, at least, for holding aplurality of substrates. This arrangement enables the wafers to betransported in carrier-based quantities.

According to yet another feature, the substrate holding section isprovided with guide grooves for directly supporting the plurality ofsubstrates. Thus, the objects are stored without using the carrier sothat the cleanbox can be made more compact and light weight.

According to yet another feature, the substrate holding section houses aplurality of substrates, and the substrate holding section is providedwith a diffuser plate for dispersing circulating air in the spacesbetween the substrates. Accordingly, cleaning of the wafers can becarried out efficiently by producing uniform flow of air in the spacesbetween the wafers.

According to yet another feature, a cleanbox recited in claim 1, inwhich the motor-driven fan is operated by a control section.Accordingly, sequences for different mode of operation may be programmedinto a microchip, so that intermittent operation may be carried out, orthe fan speed may be varied to prolong the service life of the batteryto improve the efficiency and economy of operating the cleanbox.

According to yet another feature, the container main body isstructurally integrated with constituting component parts in thecontainer main body without using fasteners. Accordingly, contaminationgenerated from the fasteners and other means of joining are preventedwhile preserving the ease of handling the components of the cleanbox formaintenance and replacement.

According to yet another feature, the container main body is maintainedat a low humidity by using a dehumidifying agent made in a sheet form orstored in a bag. Accordingly, low humidity levels in the cleanbox can beachieved quickly by circulating the air inside the cleanbox by means ofthe fan.

According to yet another feature, the gas removal filter has a filteringmembrane made of a non-woven ion exchange fabric or a woven ion exchangefabric produced by radiation-induced graft polymerization.

According to yet another feature, the gas removal filter has a filteringmembrane comprising activated charcoal produced by imbedding activatedcharcoal particulate in activated charcoal fibers or urethane foam.

According to yet another feature, the gas removal filter has a filteringmembrane comprising a combination of a gas removal filter having afiltering membrane made of a non-woven ion exchange fabric or a wovenion exchange fabric produced by radiation-induced graft polymerizationand a filtering membrane comprising an activated charcoal produced byimbedding activated charcoal particulate in activated charcoal fibers orurethane foam.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional front view of a cleanbox in a firstembodiment of this invention;

FIG. 2 is a cross sectional view through a plane A—A in FIG. 1;

FIG. 3 is a perspective view of the components of the cleanbox shown inFIG. 1;

FIG. 4 is a cross sectional front view of a cleanbox in a secondembodiment of this invention;

FIG. 5 is a cross sectional view through a plane B—B in FIG. 4;

FIG. 6 is a cross sectional front view of a cleanbox in a thirdembodiment of this invention;

FIG. 7 is a cross sectional view through a plane C—C in FIG. 6;

FIG. 8 is a front view of flow patterns obtained by computer analysis inthe third embodiment;

FIG. 9 is a side view of the flow patterns obtained by computer analysisin the third embodiment;

FIG. 10 is a graph showing changes in the concentration of gaseousammonia in the third embodiment;

FIG. 11 is a cross sectional front view of a cleanbox in a fourthembodiment of this invention;

FIG. 12 is a cross sectional view through a plane D—D in FIG. 11; and

FIG. 13 is a graph showing changes in the humidity in the fourthembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of this invention will be presented in thefollowing with reference to the drawings.

FIGS. 1-3 show a first embodiment of the cleanbox used for holding,storing and transporting a plurality of semiconductor wafers (substratesfor further processing) Wf in a carrier 10. The cleanbox is comprised bya container main body 12 of a square cylindrical shape; a lid member 14for covering the freely openable lid section at the top end of thecontainer main section; and a bottom section 16 covering the opensection at the bottom end; and hermetically sealing these componentstogether to form a hermetically sealed casing container 18. There is noneed to make the casing container 18 (including the main section 12; lidsection 14 and the bottom section 16) from expensive materials that areknown to produce low gas emission, e.g., engineering plastics orfluoride resins, which include polycarbonate, polytetrafluoroethylene,polybutylene terephthalate and polyether etherketone, for example. Thestructures used in this invention can be made from relatively low costmaterials that are easily fabricated or formed such as polypropylene,acrylonitrile butadiene styrene resins and their alloys. Antistaticagents may be included 1in the raw materials.

The interior of the casing container 18 is divided into a centralchamber 22 a and a pair of side chambers 22 b on both lateral ends ofthe central chamber 22 a by means of a pair of left and right dividingwalls 20 leaving spaces at the top and bottom ends for the lid section14 and the bottom section 16. A substrate holding section (carriersupport section) 24 having an upwardly expanding taper section isintegrally provided above the dividing walls 20 in such a way to couplewith the tapered bottom section of the carrier section 10.

An air filter 26 for removing primarily particulate matters and a gasremoval filter 28 for removing gaseous impurities are freely detachablydisposed below the substrate holding section 24 of the central chamber22 a so as to permit free flow of air in the vertical direction. In eachof the lateral chambers 22 b, a dc motor-driven brushless fan 30 isprovided so as to direct the air downwards, and a reverse flowprevention gas removal filter 32 is disposed immediately above the fan30.

The ceiling section 14 a of the lid section 14 is shaped to form asmoothly curving inside surface, and an upper laminar plate 34 of atriangular profile shape is provided in the center region. Similarly,the inner bottom section 16 a of the bottom section 16 is shaped to forma smoothly curving surface, and a bottom laminar plate 36 of atriangular profile shape is provided in its center region. A carrierentry laminar plate 38 is also provided below the substrate holdingsection 24.

Using a commonly available wafer carrier 10 of a 25-wafer storingcapacity, the spacing between the 1st wafer and the container main bodyand the spacing between the 25th wafer and the container main body aremade wider than the spacings between the wafers Wf so as not to supplythe same volume of air for all the wafers. By providing a carrier entrylaminar plate 38, air flow rates through the spaces between thecontainer main body and the 1st and 25th wafers are adjusted to beequalized in such a way that the air is supplied for all these waferseffectively.

A power feeding slot 40 a is provided on the lateral surface of thecontainer main body for freely detachably holding an electrical powerunit 40 having a terminal for connecting the power terminal to themotor-driven fan 30. The power unit 40 has an internal control device tooperate the fan 30 according to control programs to start/stop theoperation and to control the rotational speed of the fan 30.

As shown in FIG. 3, the component elements inside the cleanbox areassembled by coupling the components successively, without usingfasteners such as rivets, except for the dividing plates which areintegrally attached to the container main body. The filters 26, 28disposed in the central chamber 22 a are successively stacked on theupper frame 16 b of the bottom section 16, so as to be retained 20inside the central chamber 22 a. In the lateral chambers 22 b, a motorsupport 44 detachably attaches the motor-driven fan 30 above the upperframe 16 b, and the gas removal filter 32 is placed on top of the motorsupport 44, thereby eliminating fasteners that are potential sources ofdust particles as well as facilitating disassembly of the container 18for washing and cleaning.

In this embodiment, gas removal filter 28 is made of a woven mixture ofion exchange fibers and activated charcoal fibers, but such a part mayalso be made by wrapping a non-woven ion exchange fabric around aurethane form serving as the carrier for embedding particles ofactivated charcoal. Activated charcoal fibers may be produced bysubjecting carbon fibers made from rayon, kainol, polyacrylonitrile,kerosene, and tar pitch and reacting the fibrous carbon with steam andcarbon dioxide gas and the like at a temperature in excess of 800° C. tocarry out the so-called gasification activation process. Some activatedcharcoal fibers contain binders, that do not contribute to adsorption,for the purpose of strengthening and dust prevention, but it ispreferable that the fibers do not contain such binders from theviewpoint of their performance.

Activated charcoal contains numerous fine pores in fundamental carboncrystals because unincorporated carbons are removed in the process ofactivation. The fine pores together with the large surface area are thecontributing factors for the physical adsorption action exhibited by theactivated charcoal. Some activated charcoal filters are availablecommercially, and these use the property of strong adsorption action byimbedding activated charcoal particulate. Other commercially availablefilters for filtering air are based on activated charcoal fibers whosepores are finer than the those in the particulate types, and are readilyformable and produce less dust and offer a higher specific surface area.Other commercially available types include open pore structure fibersmade of urethane fibers, which are imbedding activated charcoalparticulate of approximately 0.5 mm diameter.

On the other hand, ion exchange fibers may be produced by introducingion exchange radicals into polymeric fibers by radiation-induced graftpolymerization reaction. Such fibers are high molecular weight polymersincluding polyethylene, polypropylene, and natural polymeric fibers suchas cotton, wool fibers or fabrics, which are subjected to radiation fromelectron beam and gamma radiation and the like to generate activationsites. These activated sites are radical sites, which are highlyreactive, however, the properties of the base fiber can be altered bychemically combining a monomer to the radical sites to produce a filtermaterial having different properties than the base fibers.

This technology is called graft polymerization because the monomers aregrafted to the base material. By radiation-induced graft polymerizationprocess, it is possible to produce non-woven ion exchange materialhaving much improved ion exchange rates than ion exchange beads whichare generally called ion exchange resins. Polyethylene non-woven fabricmay be treated by this technique by attaching ion exchange species suchas sulfone, carboxyl, and amino group monomers represented by sodiumstyrene sulfonic acid, acrylic acid or aryl amines.

Similarly, monomers that can accept ion exchange radicals such asstyrene, chlormethyl styrene, glycidylmethacrylate, acrylonitrile, oracrolein as the base may be radiation grafted and ion exchange radicalsintroduced afterwards to produce a filter that retains the originalshape.

In this embodiment, gas removal filter 28 was produced by weaving ionexchange fibers and activated charcoal fibers concurrently, but ionexchange fibers and activated charcoal fibers may be used singly or incombination to produce a gas removal filter.

Next, air filter 26 will be explained. The HEPA filter has a particlecapture efficiency in excess of 99.97% for particle of 0.3 μm size atthe standard flow rate. In the 1980s, however, with the advent of highdensity circuit integration in LSI circuits, it has become necessary todevelop filters capable of handling class 10 (10 particles/ft³)environment, and filters of higher performance than the HEPA filters. Inresponse to such a demand, ULPA filters are now available commercially.

At the beginning, glass fibers were used for ULPA filters, but a problemwas discovered that glass fibers produce BF₃ by reacting with hydrogenfluoride (HF) gas used in semiconductor processing. Recently, ULPAfilters using polytetrafluoroethylene (PTFE) as the filtering fibersthat do not contain boron and metallic impurities and do not react withacid, alkaline and organic solvents have become commercially available.In this invention, glass fibers or PTFE fibers are used as appropriate.

Next, dehumidifying agents will be explained. There are severalcommercial brands available, some of the representative substances arelisted below. Physical adsorbers available include: silica gel,molecular sieve, synthetic zeolite, and chemical adsorbers includecalcium chloride, magnesium chloride. Any of these dehumidifying agentsmay be used in the cleanbox, but it is preferable to use physicaladsorbers that give off lesser amount of contaminants in the form ofdust and organic or inorganic vapors.

The operation of the cleanbox of such a construction will be explained.The interior space of the box is maintained cleanly, and filters 26, 28,32 and the (electrical power unit are installed in their respectiveplaces. The lid section 14 is removed in a highly clean environment suchas a cleanroom so that the carrier 10 with wafers Wf can be placed onthe substrate holding section 24, and the lid section 14 is reinstalledtightly. The carrier 10 can be placed easily inside because thesubstrate holding section (carrier support section) 24 is situated abovethe filters 26, 28.

The external switch is turned on, then the motor-driven fan 30 startsoperating according to some pre-installed program. Accordingly,circulation paths are formed inside the container, descending along thelateral chambers 22 b, and ascending the central chamber 22 a, afterwhich the central stream is split in the upper region into two lateralstreams so as to descend along each of the lateral chambers 22 b andreturn separately to the fan 30. More specifically, the air streamdirected downward by the dc brushless motor-driven fan 30 flows alongthe floor 16 b of the bottom section 16, and is redirected by the lowerlaminar plate 36 so that each stream flows upward and the air streamsmerge together to form an ascending air stream through the centralregion.

The air is cleaned by flowing through both gas removal filter 28 and theULPA filter 26, and is guided between the wafers Wf by the carrier entrylaminar plate 38. By providing the carrier entry laminar plate 38,excessive flow of air between the wafers is prevented. The air streamsthat passed through the spaces between the wafers Wf are directed alongthe upper laminar plate 34 and the inner surface 14 a of the lid section14 to reverse the direction, and flow along the lateral chambers 22 b topass through the filter 32 to be cleaned and returned to the fan 30.

In the process of air circulation inside the casing container, solidparticles that may be adhering to various sections and gaseoussubstances emitted from various materials are swept by the circulatedair, and are cleaned in the two filters 26, 28 disposed in the upstreamlocation, and the air streams are then allowed to flow between thewafers Wf. Therefore, the casing container not only preventscontamination from external sources, but it aids in cleaning anysubstances that may be present in the interior space, thus preventingso-called self-contamination. Also, because the wafers are in theupstreaming location and upstream side of the lid section 14 and the lidsection 14 is susceptible to contamination from external air,contamination of the wafers caused by external sources can be prevented.

Operational mode for the fan 30 may be chosen from a variety of programmodes depending on the usage of the cleanbox. Generally, at thebeginning of the operation, the motor may be operated continuously or ata high flow rate so as to provide active cleaning of the air broughtinto the casing container. After cleaning the air in this mode, the flowrate may be lowered or the fan, may operated intermittently to preventcontamination of the wafers from the contaminants that may be generatedfrom the wafers Wf themselves or components present in the casingcontainer. This mode of operation prolongs battery life.

Here, even if contaminants are generated from the motor when the fan 30is stopped, they are prevented from reaching the wafers Wf because ofthe presence of reverse flow prevention filter 32.

FIGS. 4 and 5 show a second embodiment of this invention. The differencebetween this embodiment and the first embodiment is that the shape ofthe ceiling section 14 a of the lid section 14 is made approximately arcshaped, whose radius of curvature is greater than the radius ofcurvature of the wafers. For example, if the wafer radius R, the lidcurvature is higher than 1.2R so that the air stream flowing along theceiling section 14 a will be re-directed smoothly. Also, in thisembodiment, the carrier 10 serving as the object holder is made integralwith the object holding plate 50 so that a carrier is not needed.Opposing guide grooves 50 a are provided in the object holding plate 50to support the wafers Wf at their peripheries.

FIGS. 6 and 7 show a third embodiment of this invention. The differencebetween this embodiment and the first embodiment is that themotor-driven fan 30 is disposed on the bottom section 16, below thecentral chamber 22 a, so as to direct the air upwards. Specifically, thebottom section is provided with a support for the fan 30, and a diffuserplate 52 is disposed between the fan 30 and the gas removal filter 28 soas to disperse the air uniformly through the entire width of the centralchamber 22 a.

This design permits to use only one motor-driven fan to lighten theweight of the cleanbox. Specifically, the dimensions of the casingcontainer 18 are 250 mm width, 200 mm depth and 380 mm height to give atotal weight of 6 Kg, including twenty-five 6-inch wafers so that thecasing container can be carried by a person. The cleanbox is designed sothat the air circulating at 0.1 m³/min inside the casing container 18will produce an air speed of 0.1 m/s when flowing through the centerregion between the wafers Wf.

FIGS. 8 and 9 show the results of computer analysis of the flow patternsin the casing container of the third embodiment as seen in a front viewand a side view, respectively. The flow patterns relate to thedistribution of air speed at the exit of the fan 30 and the flow linesinside the container main body. The se flow diagrams demonstrate thatthe air filtered through the gas removal filter 28 made of weaving theion exchange fibers and activated charcoal fibers together and the ULPAfilter 26 flows between the wafers Wf uniformly without generating anystagnation inside the casing container 18.

Next, FIG. 10 shows changes that occur during the cleaning process for agiven initial concentration of ammonia. The method used was the impingermethod. It can be seen in the diagram that even when the ambientconcentration is low, the concentration is lowered to 1 ppb within 10minutes of operation.

FIGS. 11 and 12 show a fourth embodiment of this invention. Thedifferences between this embodiment and the third embodiment are thatthe power unit 40 is disposed on the bottom section 16, the gas removalfilter 32 for prevention of reverse flow is disposed at the entrance tothe fan 30, a pocket 53 for storing the dehumidifying agent is provided,and the casing container 18 is designed to be made by injection moldingto permit mass production of the cleanbox.

Such a design provides a low center of gravity in a compact and lightweight structure. The dimensions of the casing container 18 are 280 mmwidth, 220 mm depth and 360 mm height to give a total weight of 6 Kg,including twenty-five 8-inch wafers so that the casing container islighter weight than the weight of casing container in the thirdembodiment, even though the diameter of wafer has been increased.

Next, the results of measuring changes in the humidity by providing 100g of dehumidifying agent inside the fourth embodiment of the cleanboxwill be presented in FIG. 13. The results relate to a comparison of twocases, when the fan 30 was operated continuously and when the fan 30 wasstopped. The results in FIG. 13 demonstrate that it is possible to lowerthe relative humidity to about 25% by operating the fan 30 for severalminutes.

As explained above, this invention provides a cleanbox that prevents notonly external contaminants from entering the environment but alsoprevents contaminants emitted from the substrates themselves, becausethe air directed to the wafers is first cleaned by passing the airstreams through the air filter and gas removal filter, to performphysical and gas removal filtering, before the air streams are allowedto come into contact with the wafers. The cleanbox thus contributessignificantly to improving the production yield and performancequalities of those objects that must avoid contaminants caused byparticulate and gaseous substance at all cost, such as semiconductorwafers and photomasks. Because the air filter and the gas removalfilters are disposed upstream in relation to the wafer holding section,loading/unloading the wafers can be carried out from the top section ofthe casing container, and because the container lid is disposeddownstream in relation to the wafer holding section, it is possible toavoid contamination caused by the wafer holder which is susceptible tocontamination while the lid is open. Further, by including thehumidifying agent inside the box and circulating air in the box, thehumidity inside the box can be lowered in a short time to a relativehumidify value that is less than 25% to contribute to reducing thechemical reaction of the wafers with an ambient atmosphere.

Industrial Applicability

This invention is useful for cleanbox used to store or transport objectssuch as semiconductor wafers and photomasks, for example, until they areneeded for processing in cleanrooms.

What is claimed is:
 1. A cleanbox comprising: a casing containercomprised by a container main body and a lid member for covering anopening of the container main body; a pair of dividing walls disposed insaid container main body, an air filter and a gas removal filterdisposed between said dividing walls; a substrate holding section havinga pair of object holding plates for holding peripheral portions ofsubstrates therebetween; an air flow path defined between said dividingwalls and between said object holding plates; and a motor-driven fanhoused in the casing container for producing air streams circulatingbetween said dividing walls, and between said object holding plates andan outside thereof.
 2. A cleanbox according to claim 1, wherein saidpair of object holding plates comprises a pair of side-walls of a wafercarrier, which wafer carrier accommodates a plurality of substratesapproximately parallel to the air flow path.
 3. A cleanbox according toclaim 2, wherein said wafer carrier is placed on a carrier supportsection, which is integrally formed with said pair of dividing walls. 4.A cleanbox according to claim 1, wherein said pair of object holdingplates is integrally formed with said pair of dividing walls.
 5. Acleanbox according to claim 1, wherein said air flow path is defined atat least one of a top section and a bottom section of-said casingcontainer by a spherical arc surface.
 6. A cleanbox according to claims5, wherein an inner surface of said lid member and a bottom surface ofsaid container main body are provided with guiding protrusions forseparating the air flow path.
 7. A cleanbox according to claim 1,wherein said air streams are provided with a reverse flow preventingfilter in a downstream location to the substrates so as to prevent backstreaming of contaminants from the motor-driven fan.
 8. A cleanboxaccording to claim 1, wherein each of said object holding plates isprovided with guide grooves for holding a plurality of substrates.
 9. Acleanbox according to claim 1, wherein said substrate holding sectionhouses a plurality of substrates, and said substrate holding section isprovided with a diffuser plate for dispersing circulating air in spacesbetween the substrates.
 10. A cleanbox according to claim 1, including acontrol section for said motor-driven fan.
 11. A cleanbox according toclaim 1, wherein said container main body is structurally integratedwith constituting component parts in the container main body withoutusing fasteners.
 12. A cleanbox according to claim 1, including adehumidifying agent in said container main body.
 13. A cleanboxaccording to claim 12, wherein said dehumidifying agent is one of asheet and an agent stored in a bag.
 14. A cleanbox according to claim 1,wherein said gas removal filter has a filtering membrane made of one ofa non-woven ion exchange fabric and a woven ion exchange fabric.
 15. Acleanbox according to claim 1, wherein said gas removal filter has afiltering membrane comprising one of activated charcoal and activatedcharcoal fibers.
 16. A cleanbox according to claim 1, wherein said gasremoval filter has a filtering membrane comprising a combination of agas removal filter having a filtering membrane made of a non-woven ionexchange fabric or a woven ion exchange fabric, and a filtering membranecomprising an activated charcoal or activated charcoal fibers.
 17. Acleanbox according to claim 1, including a power unit outside of saidcasing container for supplying power to said motor-driven fan.
 18. Acleanbox according to claim 17, wherein said power unit is detachablymounted on said casing container.
 19. A cleanbox according to claim 17,including a terminal for connecting said power unit provided on alateral surface of said casing container.
 20. A cleanbox according toclaim 1, including a control section provided for operating saidmotor-driven fan.
 21. A cleanbox according to claim 1, including acontrol section provided for operating said motor-driven fan for one ofintermittent and variable speed operation.
 22. A cleanbox according toclaim 20, wherein said control section includes a microchip.
 23. Acleanbox according to claim 21, wherein said control section includes amicrochip.
 24. A cleanbox according to claim 20, wherein said controlsection operates said motor-driven fan continuously or at a high flowrate at a beginning of operation, and intermittently or at a low flowrate thereafter.
 25. A cleanbox according to claim 1, wherein a motor ofsaid motor-driven fan comprises a dc brushless motor.
 26. A cleanboxaccording to claim 1, wherein a motor of said motor-driven fan ishermetically sealed in a casing.
 27. A cleanbox comprising: a casingcontainer comprised by a container main body and a lid member forcovering an opening of the container main body; a substrate holdingsection having a pair of object holding plates for holding peripheralportions of substrates therebetween; a first air flow path definedbetween inner surfaces of said object holding plates; a second air flowpath defined between an outer surface of said object holding plates andan inner surface of said casing container; a motor-driven fan housed inthe casing container for producing air streams circulating through saidfirst air flow path and said second air flow path; and an air filter anda gas removal filter disposed in said circulating air streams.
 28. Anapparatus for transporting substrates comprising: a casing containercomprised by a container main body and a lid member for covering anopening of the container main body; dividing walls disposed in a saidcontainer main body, an air filter and a gas removal filter disposedbetween said dividing walls; a substrate holding section disposed insaid casing container having a pair of object holding plates for holdingperipheral portions of substrates therebetween; an air flow path definedbetween said dividing walls and said object holding plates; and amotor-driven fan housed in the casing container for producing airstreams circulating between said dividing walls and said object holdingplates.
 29. An apparatus according to claim 28, wherein said pair ofobject holding plates comprises a pair of side-walls of the wafercarrier.
 30. An apparatus according to claim 29, wherein said wafercarrier is placed on a carrier support section, which is integrallyformed with said pair of dividing walls.
 31. An apparatus according toclaim 28, wherein said pair of object holding plates is integrallyformed with said pair of dividing walls.
 32. An apparatus according toclaim 28, wherein said air flow path is defined at least one of a topsection and a bottom section of said casing container by a spherical aresurface.
 33. An apparatus according to claim 32, wherein an innersurface of said lid member or a bottom surface of said container mainbody is provided with guiding protrusions for separating the air flowpath.
 34. An apparatus according to claim 28, wherein said air streamsare provided with a reverse flow preventing filter in a downstreamlocation to the substrates so as to prevent back streaming ofcontaminants from the motor-driven fan.
 35. An apparatus according toclaim 28, wherein each of said object holding plates is provided withguide grooves for holding a plurality of substrates.
 36. An apparatusaccording to claim 28, wherein said substrate holding section houses aplurality of substrates, and said substrate holding section is providedwith a diffuser plate for dispersing circulating air in spaces betweenthe substrates.
 37. An apparatus according to claim 28, including acontrol section for said motor-driven fan.
 38. An apparatus according toclaim 28, wherein said container main body is structurally integratedwith constituting component parts in the container main body withoutusing fastners.
 39. An apparatus according to claim 28, furtherincluding a dehumidifying agent in said container main body.
 40. Anapparatus according to claim 39, wherein said dehumidifying agent is oneof a sheet and an agent stored in a bag.
 41. An apparatus according toclaim 28, wherein said gas removal filter has a filtering membrane madeof one of a non-woven ion exchange fabric and a woven ion exchangefabric.
 42. An apparatus according to claim 28, wherein said gas removalfilter has a filter membrane comprising one of activated charcoal andactivated charcoal fibers.
 43. An apparatus according to claim 28,wherein said gas removal filter has a filtering membrane comprising acombination of a gas removal filter having a filtering membrane made ofa non-woven ion exchange fabric or a woven ion exchange fabric, andhaving a filtering membrane comprising an activated charcoal oractivated charcoal fibers.
 44. An apparatus according to claim 28,including a power unit outside of said casing container for supplyingpower to said motor-driven fan.
 45. An apparatus according to claim 44,wherein said power unit is detachably mounted on said casing container.46. An apparatus according to claim 44, including a terminal forconnecting said power unit provided on a lateral surface of said casingcontaining.
 47. An apparatus according to claim 28, including a controlsection provided for operating said motor-driven fan.
 48. An apparatusaccording to claim 28, including a control section provided foroperating said motor-driven fan for one of intermittent and variablespeed operation.
 49. An apparatus according to claim 47, wherein saidcontrol section includes a microchip.
 50. An apparatus according toclaim 48, wherein said control section includes a microchip.
 51. Anapparatus according to claim 47, wherein said control section operatessaid motor-driven fan continuously or at a high flow rate at a beginningor operation, and intermittently or at a low flow rate thereafter. 52.An apparatus according to claim 28, wherein a motor of said motor-drivenfan comprises a dc brushless motor.
 53. An apparatus according to claim28, wherein a motor of said motor-driven fan is hermetically sealed in acasing.
 54. A cleaning box comprising: a casing container conprised by acontainer main body and a lid member for covering an opening of thecontainer main body; a pair of dividing walls disposed in said containermain body, an air filter and a gas removal filter disposed between saiddividing therebetween; an air flow path defined between said dividingwalls and between said object holding plates; and a circulating devicehoused in the casing container for producing air streams circulatingbetween said dividing walls and said object holding plates.
 55. A cleanbox for transporting substrates comprising: a casing container comprisedby a container main body and a lid member for covering an opening of thecontainer main body; a pair of dividing walls disposed in said containermain body; a substrate holding section having a pair of object holdingplates for holding peripheral portions of the substrates therebetween inthe casing container; an air flow path defined between said dividingwalls and said object holding plates; a filter disposed outside of saiddividing walls and said object holding plate and inside wall of saidcontainer main body; and a circulation in the casing container forproducing air streams through between said dividing walls and saidobject holding plates, and said filter.
 56. An apparatus according toclaim 55, wherein said circulation device is disposed outside of saiddividing wall and/or said object holding plate and inside of saidcontainer main body.
 57. A clean box for carrying substrate comprising:a casing container comprised by a container main body and a lid memberfor covering an opening of the container main body; a substrate holdingsection having a pair of object holding plates for holding peripheralportions of the substrates therebetween in the casing container; firstair flow path defined between said object holding plates; second airflow path defined between said object holding plate and inside wall ofsaid container main body; a filter disposed between said object holdingplate and inside wall of said container main body; and a circulationdevice in the casing container for producing air streams though saidfirst air flow path, said second air flow path and said filter.
 58. Anapparatus according to claim 57, wherein said circulation device isdisposed outside of said object holding plate and inside of saidcontainer main body.